1. Field of the Invention
The invention is directed to a refrigeration system using a capillary tube as a restriction device, and, more specifically, to a capillary tube having a variable inner cross-sectional area to prevent deposits of contaminants from the refrigerant from clogging the capillary tube.
2. Description of the Related Art
Contemporary refrigeration systems are well known and understood. Typically, a conventional refrigeration system comprises a compressor, condenser, restriction device, and evaporator all connected in series. The condenser is connected to the outlet or high pressure side of the compressor, whereas the evaporator is connected to the inlet or suction side of the compressor. The restriction device, such as a capillary tube, connects the condenser to the evaporator.
In operation, the compressor compresses a refrigerant and expels it into the condenser. The flow of the refrigerant is restricted as it encounters the capillary tube, resulting in an increase in the pressure of the refrigerant in the condenser. As the compressed and high pressure refrigerant exits the capillary tube and enters the low pressure and greater volume environment of the evaporator, the refrigerant expands and boils, resulting in a temperature decrease in the evaporator. The refrigerant, now generally in a gaseous state, then moves toward the compressor, where it is once again compressed and the cycle repeated. In some systems, the capillary tube and the tube that returns the refrigerant to the compressor are soldered together to form a heat exchanger (often called a suction line heat exchanger ). This improves the energy efficiency of the refrigeration system.
One disadvantage of this process is that during the expansion of the refrigerant as it leaves the capillary tube and enters the evaporator, the change of state of the refrigerant from a liquid to a gas and its associated temperature decrease results in contaminants contained in the refrigerant being deposited within a portion of the capillary tube near the junction of the evaporator. Over time, these deposits can result in a clogging of the capillary tube and a reduction in performance of the refrigeration system. The problem of contaminants clogging the capillary tube is much worse when using newer refrigerants, such as R-134A (HFC). The HFC systems are particularly vulnerable to hydrocarbon contaminants, especially paraffins, which can clog the sealed refrigeration system, causing it to fail.